Ignoring the core principle of Capitalism, free markets, makes it impossible to actually talk about Capitalism in theory or in practice.

The confusion comes from the fact that the word capitalism has two meanings. The original meaning, which the other person and myself are using, has nothing to do with free markets:

1854, “condition of having capital;” from capital (n.1) + -ism. The meaning “political/economic system which encourages capitalists” is recorded from 1872 and originally was used disparagingly by socialists. The meaning “concentration of capital in the hands of a few; the power or influence of large capital” is from 1877.

It was only later, in reaction to socialism, that capitalism began to take on this meaning you’re using, where it’s supposedly disconnected from class interests and is just about some abstract economic principle. But using the second definition, it’s impossible to talk about capitalism in practice because, as I said, such a system has never existed and will never exist.

Your argument against can be used for every other economic system as well, so it becomes a matter of pros and cons which will never declare a clear winner and always demonstrate a mixed economy is best for everyone involved.

Huh? Economic systems where the interests of capitalists are prioritized are best for the capitalists, economic systems where the interests of workers are prioritized are the best for workers. Also, aren’t you declaring a clear winner when you say you can, “always demonstrate a mixed economy is best for everyone involved?”